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NORLEX


Borr Member

Rogaland Group, Våle Formation

Unit definition

The Borr Member is attributed to the intra Våle Formation sandstones in the subarea of the Norwegian Danish Basin to the Søgne Graben and the southeasternmost part of the Central Trough, (Figs. 12, 13 and 48).

Name

The name Borr Member has been informally attributed to the sandstones in the lower part of the Våle Formation in the Siri Valley, Danish North Sea since the sandstones were discovered by Statoil in the mid 1990s. The sands are time equivalent to the lower Ty sands in the Viking Graben and the Maureen Member of the Central Trough. For the Norwegian North Sea we extend the definition to account for all easterly derived sandstones in the Central Trough, Siri Valley and the Norwegian Danish Basin that are enclosed in the Våle Formation.

Derivatio nominis

The Borr Member is named after Borr who was a Giant in the norse myths in Voluspá and Gylfaginning.

Type well

For the Danish sector, Schiøler et al. (2007) have defined the DK well Augusta-1 as the type well for the Borr Member (Fig. 55): Depth 2963.2-2940.5 m RKB. Coordinates N 56°17'57.40", E 04°24'04.64". Cores no. 1, 2923.5-2889 m RKB.

Fig. 55. DK Wells Augusta-1 (Type Well) and Cecilie-1 (reference well) composites log Rogaland Group. Position of the Borr Member is seen in 2nd column from left. Modified from Schiøler et al. 2007 to fit definitions made in the nomenclature for Norwegian North Sea (this paper).

Fig. 56. Well 3/7-4 composite log Rogaland Group. Stratigraphic position of the Borr Member is outlined in stratigraphic column to the right.

Reference wells

Norwegian well 3/7-4 (New) (Fig. 56). Depth 2815-2845 m RKB. Coordinates N 56°24'15.60", E 04°14'22.24". In this study we select 3/7-4 as a reference well for the Borr Member, Norwegian North Sea. So far there are no cores from the Borr Member in any Norwegian wells.

Reference well for Danish sector: Cecilie-1 (Fig. 55). Depth 2319.6-2284.6 m RKB. Coordinates N 56°24'23.73", E 04°45'42.00". Cores 2230-2336.4 m RKB.

A suitable reference section for the Borr Member is Norwegian well 3/6-1 (Fig. 57). Depth 2051-2092 m. Coordinates N 56°35'00.14", E 04°53'30.35". No cores from the Borr Member.

Fig. 57. Well 3/6-1 composite log Rogaland Group. Stratigraphic position of the Borr Member is outlined in stratigraphic column to the right.

Composition

The Borr Member consists of olive-green, massive, clean sandstones of grain size varying from very fine to fine grained. The sandstones are quartzitic and glauconitic (up to 25%), and often calcite cemented, especially when sand layer thickness is limited. Mica and pyrite are also present in small amounts.

Wireline log characterization

The wireline log appearance of the sandstones of the Borr Member relative to the Våle Formation above and below is variable. The response may be blocky, easily distinguishable with low gamma-ray readings, to more subtle fine grained sands with a gradual transition from clay and silt into very fine sand. From sonic and density logs thin bedded sandstones are often carbonate cemented.

Lower boundary

The Borr Member rests on the marly shales of the Våle Formation or directly on the Shetland Group chalks. When the sandsones rest on the Shetland Group or a very calcareous Våle Formation there is an upwards change from low gamma-ray readings and high velocities in the calcareous sediments to higher gamma-ray readings and lower velocities in the Borr Member. The lower boundary of the Borr Member can often be difficult to pick when the Våle Formation is calcareous because the gamma-ray values in the two stratigraphic units can sometimes be very similar.

When the Borr Member rests on less calcareous Våle Formation the response will depend on the calcareous content. There is an upwards change from intermediate to low gamma-ray readings and high velocities in the calcareous sediments to higher gamma-ray readings and lower velocities in the Borr Member.

Upper boundary

The upper boundary is usually characterised by a downwards transition from somewhat higher gamma-ray readings and lower velocity in the Våle or Lista Formation to lower gamma-ray readings and higher velocity in the Borr Member.

Thickness

In the Norwegian North Sea the Borr Member is generally rather thin, and in the wells a maximum thickness of 29 m is found in Norwegian well 3/7-3. In the Danish sector in the Siri Valley sand fairway, the Borr Member reaches 24 m in Cecilie-1.

Seismic characterization

The top of the Borr Member is sometimes seismically well defined, and can be mapped out sub regionally. Seismic character varies between one cycle sub-parallel to mounded facies. Sometimes thicker infill of depressions or canyons in the substratum can be seen. Seismic 3D amplitude maps of near top or base Våle formation sometimes display channel or fan shaped geometries that represent submarine channels or fan systems. A seismic cross section example from the southwestern part of the Søgne Graben is shown in Fig. 58, and a seismic attribute map in Fig 59.

Fig. 58. Seismic SW/NE section through the Trym salt collapse structure, showing sandy interval of the Borr Member filling in a collapse feature.

Fig. 59. Seismic map from block 3/7 and 3/8, showing amplitude at Top Våle Level. Red color shows high amplitude, and inferred presence of Borr sandstone (proven in wells).

Age

Lower to Middle Paleocene (Danian-Early Selandian).

Biostratigraphy

Being contained in the Våle Formation, the age of the Borr Member is bounded by biostratigraphy and age assignments for the Våle Formation. See description for the Våle Formation in Subchapter 4.1.

Correlation and subdivision

The Borr Member is divided into Borr V1 Sub-member (Lower Borr Member) and Borr V2 Sub-member (Upper Borr Member), following the subdivision of the Våle Formation.

Geographic distribution

The Borr Member is deposited in the Norwegian Danish Basin and the Siri Valley fairway, and appears to have some offshoots westward into the Søgne Graben and the Central Trough (Fig. 48), where it is found in Norwegian wells 3/7-2, -3, -4. It is uncertain how far north the Borr sandstones are distributed, but from seismic, mounded characters are seen far north in the Egersund Basin which possibly indicates that the Borr Member is also present in that area.

Occurrences of member tops in wells

Depositional environment

The Borr Member is generally believed to have been deposited in a slope to deep marine setting, mainly as highly concentrated gravity flow deposits. In eastern areas of the Norwegian Danish basin, parts of the Borr Member may even have been deposited in a shelfal to shallow marine environment.

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